Flavor Composition or Fragrance Composition, and Flavor-Improving Agents

ABSTRACT

The present invention relates to a flavor composition or fragrance composition which can satisfy diversified requirements for flavored products, as well as to a flavor-improving agent which can improve the quality and release of aroma of a beverage or food. More particularly, the present invention relates to a flavor composition or fragrance composition which comprises an optically active S-alkyl 2-methylbutanethioate as an active ingredient, a flavor- or fragrance-added product, a flavor-improving agent which comprises an optically active S-alkyl 2-methylbutanethioate as an active ingredient, and a beverage or food having an improved flavor. The optically active S-alkyl 2-methylbutanethioate includes S-alkyl (R)-2-methylbutanethioate and S-alkyl (S)-2-methylbutanethioate.

TECHNICAL FIELD

The present invention relates to a flavor composition or fragrancecomposition which can satisfy diversified requirements for flavoredproducts, as well as to a flavor-improving agent which can improve thequality and release of odor of a beverage or food. More particularly,the present invention relates to a flavor composition or fragrancecomposition which comprises an optically active S-alkyl2-methylbutanethioate as an active ingredient, a flavor- orfragrance-added product, a flavor-improving agent which comprises anoptically active S-alkyl 2-methylbutanethioate as an active ingredient,and a beverage or food having an improved flavor.

BACKGROUND ART

Many of the compounds which have been used as a flavor component, afragrance component or a flavor-improving agent in beverages, foods,cosmetics, etc., are racemic forms. For example, S-alkyl2-methylbutanethioates are known to be pre-sent as racemic forms innatural products, particularly in fruits and beer (non-patentliteratures 1 to 13). Of these racemic S-alkyl 2-methylbutanethioates,S-methyl 2-methylbutanethioate, in particular, is in use for the purposeof providing, for example, an odor of food fermentation or a feeling ofripe fruit.

The flavor component or fragrance component comprising such a racemicS-alkyl 2-methylbutanethioate as an active ingredient is satisfactory tosome extent in that it provides a good fermentation odor or a feeling ofripe fruit; however, it is not sufficient. Also, the flavor-improvingagent comprising the racemic S-alkyl 2-methylbutanethioate as an activeingredient, still has much room for improvement in release of odor.

Meanwhile, in connection with the analysis of the odorous component ofcheese, there was made a chromatographic analysis on S-methyl(S)-2-methylbutanethioate and racemic S-methyl 2-methylbutanethioate,and their odor characteristics were reported (non-patent literature 14).Also, in connection with the analysis of the odorous component of hop,the odor characteristic of racemic S-methyl 2-methylbutanethioate wasreported. (non-patent literature 8).

According to the descriptions in these literatures, the odorcharacteristic of racemic S-methyl 2-methylbutanethioate is wildstrawberry (non-patent literature 14), or cooked vegetable, sulphury orsoapy/fatty (non-patent literature 8), and the odor characteristic ofS-methyl (S)-2-methylbutanethioate is rubbery (non-patent literature14).

However, none of these reports mentions the odor of S-alkyl(R)-2-methylbutanethioate, such as S-methyl (R)-2-methylbutanethioate.Further, each of these reports evaluated only the odor characteristicsof single compounds, having no direct connection with the flavors ofbeverages or foods, and made no evaluation on the flavors and odorreleases when S-alkyl (S)-2-methylbutanethioate had been actually usedin beverages or foods (although, in these reports, there aredescriptions on S-alkyl (S)-2-methylbutanethioate).

Non-patent literature 1: Food Chemistry (2000), 69 (3), 319-330

Non-patent literature 2: Journal of the Institute of Brewing (1983), 89(2), 87-91

Non-patent literature 3: Proceedings of the Congress-European BreweryConvention (1981), 18th, 161-8

Non-patent literature 4: Proceedings of the Congress-European BreweryConvention (1979), 17th, 79-89

Non-patent literature 5: Proceedings of the Congress-European BreweryConvention (1981), 17th, 91-104

Non-patent literature 6: Technical Quarterly-Master Brewers Associationof the Americas (1981), 18(1), 26-30

Non-patent literature 7: Organic Magnetic Resonance (1979), 12(10),557-60

Non-patent literature 8: Proceedings of the Analytical Division of theChemical Society (1976), 13(7), 215-17

Non-patent literature 9: Journal of Organic Chemistry (1973), 38 (24),4239-43

Non-patent literature 10: Flavour and Fragrance Journal (1996), 11 (5),295-303

Non-patent literature 11: Tetrahedron Letters (1971), (30), 2837-8

Non-patent literature 12: Development in Food Science (1988), 18(Flavors Fragrances), 573-85

Non-patent literature 13: Abstrack book of 32^(nd) Symposium on theChemistry of Terpenes, Essential oils, Aromatics, 31 to 33 pages, Oct.24, 1988.

Non-patent literature 14: Lebensmittel-Wissenschaft und-Technologie(1979), 12 (5), 258-61

DISCLOSURE OF THE INVENTION Task to Be Achieved by the Invention

The present invention has been made under the background of theabove-mentioned prior art and aims at providing a highly-taste, superiorflavor composition or fragrance composition which can satisfydiversified requirements for flavored products, and a flavor-improvingagent which can improve the quality and release of the odor of beverageor food.

Means for Achieving the Task

The present invention has achieved the above task by the following (1)to (18).

(1) A flavor composition or fragrance composition and a flavor-improvingagent, characterized by comprising an optically active S-alkyl2-methylbutanethioate as an active ingredient.(2) A flavor composition or fragrance composition characterized bycomprising an S-alkyl (R)-2-methylbutanethioate as an active ingredient.(3) A flavor composition or fragrance composition according to (2),wherein the S-alkyl (R)-2-methylbutanethioate has an optical purity of50% e.e. or more.(4) A flavor composition or fragrance composition according to any of(1) to (3), which is a flavor composition.(5) A flavor composition characterized by comprising an S-alkyl(R)-2-methylbutanethioate at a concentration of 10⁻⁶ to 10⁷ ppb.(6) A product added with a flavor by a flavor composition set forth in(5).(7) A flavor-added product according to (6), which is one memberselected from beverages, foods, oral-care compositions and medicines.(8) A product added with a flavor, characterized by being obtained byadding an S-alkyl (R)-2-methylbutanethioate at a concentration of 10⁻⁹to 10⁵ ppb.(9) A flavor composition or fragrance composition according to any of(1) to (3), which is a fragrance composition.(10) A fragrance composition characterized by comprising an S-alkyl(R)-2-methylbutanethioate at a concentration of 10⁻⁶ to 10⁷ ppb.(11) A product added with a fragrance by a fragrance composition setforth in (10).(12) A fragrance-added product according to (11), which is one memberselected from fragrance products, skin-care preparations, make-upcosmetics, hair cosmetics, sunblock cosmetics, medicated cosmetics,hair-care products, soaps, body cleaners, bath preparations, detergents,fabric softeners, cleaning agents, kitchen cleaners, bleaching agents,aerosols, deodorant-aromatics, repellants and sundries.(13) A product added with a fragrance, characterized by being obtainedby adding an S-alkyl (R)-2-methylbutanethioate at a concentration of10⁻⁹ to 10⁷ ppb.(14) A method for intensification, improvement or modification of flavoror fragrance, characterized by adding an S-alkyl(R)-2-methylbutanethioate.(15) A flavor-improving agent characterized by comprising, as an activeingredient, an S-alkyl (S)-2-methylbutanethioate having an opticalpurity of 70% e.e. or more.(16) A flavor-improving agent according to (15), wherein the S-alkyl(S)-2-methylbutanethioate is S-methyl (S)-2-methylbutanethioate.(17) A beverage or food having an improved flavor, characterized bycomprising an S-alkyl (S)-2-methylbutanethioate having an optical purityof 70% e.e. or more, at a proportion of 10⁻⁸ to 10⁵ ppb when convertedto 100% optical purity.(18) A beverage or food having an improved flavor according to (17),wherein the S-alkyl (S)-2-methylbutanethioate is S-methyl(S)-2-methylbutanethioate.

Under the above-mentioned situation, the present inventors made anextensive study. As a result, it was found that the above task could beachieved by optically active S-alkyl 2-methylbutanethioates and not byracemic S-alkyl 2-methylbutanethioates used widely in the market.Specifically explaining, it was first found that the flavor compositionor fragrance composition comprising an S-alkyl (R)-2-methylbutanethioateas an active ingredient has a flavor or fragrance which is strong andfresh, and reminds a passion fruit, well harmonizes with the flavorcomponent or fragrance component used together, and can impart abeautiful, fresh, highly-taste flavor or fragrance which has beeninsufficient with known similar compounds derived from natural orprocessed beverages or foods.

The flavor composition or fragrance composition of the present inventioncomprising an S-alkyl (R)-2-methylbutanethioate as an active ingredienthas a flavor or fragrance which is strong and fresh, and reminds apassion fruit, well harmonizes with the flavor composition or fragrancecomponent used together, and can impart a beautiful, fresh, highly-tasteflavor or fragrance which has been insufficient with known similarcompounds derived from natural or processed beverages or foods.Therefore, the flavor composition or fragrance composition of thepresent invention can be used widely in the flavor- or fragrance-addedproducts of the present invention, food materials, food additives,insurance or sanitary materials, etc.

The present inventors further found that the flavor-improving agent ofthe present invention comprising an S-alkyl (S)-2-methylbutanethioate asan active ingredient, when added to various beverages or foods such asfruit juice drinks, foods and the like, provides a very clear, highlyvolatile odor reminding ripe fruits, gives an intensified flavor, canprovide a beverage or a food both very superior in flavor and/orfragrance, and therefore can enhance the commercial value of the abovebeverages or foods. The study was continued and the present inventionhas been completed.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below.

In the present invention, racemic S-alkyl 2-methylbutanethioates usedwidely in the market are not used but optically active S-alkyl2-methylbutanethioates are used. First, in the flavor composition orfragrance composition of the present invention, S-alkyl(R)-2-methylbutanethiontes are used as an essential component. Asspecific examples of the S-alkyl (R)-2-methylbutanethioates, there canbe mentioned S-methyl ester, S-ethyl ester, S-n-propyl ester,S-isopropyl ester, S-butyl ester, S-2-methylpropyl ester, S-pentylester, S-2-methylbutyl ester, S-3-methylbutyl ester, S-hexyl ester,S-cis-3-hexenyl ester, S-heptyl ester and S-octyl ester of(R)-2-methylbutanethioic acid.

The S-alkyl (R)-2-methylbutanethioates may be used as an essentialcomponent, in one kind or in two or more kinds. Of these compounds, acompound preferred as the essential component of the flavor compositionor fragrance composition of the present invention is S-methyl(R)-2-methylbutanethioate.

The S-alkyl (R)-2-methylbutanethioate used in the pre-sent invention maybe obtained by extraction from natural product, or by optical resolutionof racemic form, or may be obtained by chemical synthesis. However, whenthe S-alkyl (R)-2-methylbutanethioate is used in a large amount, it isobtained preferably by chemical synthesis.

For chemical synthesis of S-alkyl (R)-2-methylbutanethioate, there canbe mentioned, for example, a method of converting (R)-2-methylbutanoicacid (a raw material) into an acid halide and then reacting it with analkyl-thiol.

For chemical synthesis of (R)-2-methylbutanoic acid, there can bementioned, for example, a method described in JP-A-1988-239245, that is,a method of using, as a raw material, tiglic acid[(E)-2-methyl-2-butenoic acid] easily obtainable as a commercial productand subjecting it to asymmetric hydrogenation using, as a catalyst, aruthenium-optically active phosphine complex having a particularabsolute configuration.

The above chemical synthesis method for (R)-2-methylbutanoic acid isdescribed in more detail. Tiglic acid is dissolved in a solvent such asmethanol or ethanol; the solution is fed into an autoclave purged withan inert gas; thereto is added a ruthenium-optically active phosphinecomplex of 1/100 to 1/1,000 mole per mole of tiglic acid; andhydrogenation is conducted with stirring, at a hydrogen pressure of 4 to125 kg/cm² at a temperature of 5 to 50° C. for 1 to 100 hours.

There may also be used a method of using no hydrogen gas as a hydrogensource, described in JP-A-1991-157346. In this method, there is used, asa hydrogen donor, a large excess of a primary or secondary alcohol.After the reaction, the solvent is distilled off and the residue issubjected to distillation under reduced pressure, whereby intended(R)-2-methylbutanoic acid can be obtained.

Incidentally, as the ruthenium-optically active phosphine complex whichcan be used, there can be mentioned, for example, the followingcompounds.

Ru_(x)H_(y)Cl_(z)[(+)-(R—BINAP)]₂(S)_(p)  (1)

{wherein (+)-(R—BINAP) is(−)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl,(+)-2,2′-bis(di-p-methylphenylphosphino)-1,1′-binaphthyl or the like; Sis a tertiary amine; y is 0 or 1; when y is 0, x is 2, Z is 4, and p is1; when y is 1, x is 1, Z is 1, and p is 0.}

{Ru[(+)-(X—BINAP)]_(q)}(OCOR¹)(OCOR²)  (2)

{wherein (+)-(X—BINAP) is(+)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl wherein the two naphthylgroups may be substituted, at the 5- and 5′-positions, with amino group,acetylamino group or sulfone group and the four phenyl groups may besubstituted with lower alkyl group at the p-position; R¹ and R² are eacha lower alkyl group, a halogenated lower alkyl group, a phenyl groupwhich may be substituted with lower alkyl group, an α-aminoalkyl group,or an α-aminophenylalkyl group, or, R¹ and R² may be combined togetherto form an alkylene group; q is 1 or 2.}

{RuH₁[(+)-(R—BINAP)]_(v)}Y_(w)  (3)

{wherein (+)-(R—BINAP) is the same as defined above; Y is ClO₄, BF₄ orPF₆; 1 is 0 or 1; when 1 is 0, v is 1 and w is 2; when 1 is 1, v is 2and w is 1.}

{Ru[(+)-(BIPHEMP)]}Y₂  (4)

{wherein (+)-(BIPHEMP) is(−)-2,2′-dimethyl-6,6′-bis(diphenylphosphino)-1,1′-biphenyl,(−)-2,2′-dimethyl-6,6′-bis(di-p-methylphenylphosphino)-1,1′-biphenyl,(−)-2,2′-dimethyl-6,6′-bis(di-p-methoxyphenylphosphino)-1,1′-biphenyl orthe like; Y is the same as defined above.}

The above-shown ruthenium-optically active phosphine complexes of (1) to(3) can each be obtained by the method described in JP-A-1988-239245.The ruthenium-optically active phosphine complex of (4) is a complexdescribed in JP-A-1988-145292.

In the flavor composition or fragrance composition of the presentinvention, the S-alkyl (R)-2-methylbutanethioate obtained as above ispreferred to have an optical purity of 50% e.e. ore more.

The S-methyl (R)-2-methylbutanethioate synthesized according to themethod described in JP-A-1988-239245 had a high optical purity of about88% e.e. A test was conducted to examine the optical purity of S-methyl(R)-2-methylbutanethioate at which the (R) isomer began to show itseffect. As a result, it was found that the (R) isomer begins to show theeffect at an optical purity of about 50% e.e. Based on this result, itwas anticipated that the effect of the present invention can be reliablyexpected also for other thioesters when their optical purities are 50%e.e. or more. Accordingly, it was found that the (R)-thioesters havingan optical purity of 50% e.e. or more can be used per se with nopurification, as the essential component of the present flavorcomposition or fragrance composition and can provide various cosmetics,beverages or foods reliably releasing a fragrance or a flavor.

As seen in Examples shown later, the flavor composition or fragrancecomposition of the present invention containing an S-alkyl(R)-2-methylbutanethioate, for example, as an active ingredient shows astrong, fresh flavor or fragrance which reminds a passion fruit. TheS-alkyl (R)-2-methylbutanethioate (which is an active ingredient)exhibits an effect even at a small content and, therefore, can impart aflavor or fragrance to the base materials of various cosmetics,beverages or foods, to be imparted with a flavor or fragrance by aflavor composition or fragrance composition. Meanwhile, racemic S-methyl2-methylbutanethioate has a natural aroma, but is low in strength, hasslight other odors, and has no sufficient effect.

The flavor composition or fragrance composition of the present inventioncontaining an S-alkyl (R)-2-methylbutanethioate, for example, as anactive ingredient has, as mentioned above, a widely accepted, superior,strong, fresh flavor or fragrance which reminds a passion fruit and,moreover, has a striking durability and stability for flavor orfragrance. Therefore, by adding the S-alkyl (R)-2-methylbutanethioate,there can be provided a flavor composition or fragrance compositionwhich is accepted widely.

In the flavor composition or fragrance composition of the presentinvention, there can be used, in addition to the active ingredient withS-alkyl (R)-2-methylbutanethioate or the like, for example, a flavorcomponent and/or a fragrance component ordinarily used. As the otherflavor component and/or fragrance component usable, there can bementioned various synthetic aromachemicals, natural essential oils,synthetic essential oils, citrus oils, animal aromachemicals, etc.Particularly preferred are flower-based or fruit-based flavor componentsand/or fragrance components; and there can be used, for example, a widerange of flavor components and/or fragrance components, such asdescribed in, for example, Arctander S., “Perfume and Flavor Chemicals”,published by the author, Montclair, N.J. (U.S.A), 1969. Asrepresentative other components, there can be mentioned α-pinene,limonene, cis-3-hexenol, phenylethyl alcohol, styrallyl acetate,eugenol, rose oxide, linalool, benzaldehyde, muscone, Thesaron (aproduct of Takasago International Corporation), ethyl butyrate,2-methylbutanoic acid, etc.

Illustratively, when the S-alkyl (R)-2-methylbutanethioate is added tonatural essential oil, for example, bergamot oil, galbanum oil, lemonoil, geranium oil, lavender oil, mandarin oil or the like, there can beprepared a novel flavor composition or fragrance composition having, inaddition to the flavor and/or fragrance inherently possessed by thenatural essential oil, a flavor and/or fragrance which is mild, deep,fresh and highly-taste and which has durability and holding abilitythere of are enhanced.

When the S-alkyl (R)-2-methylbutanethioate is added to a flavorcomposition or fragrance composition such as strawberry, lemon, orange,grapefruit, apple, pineapple, banana, melon, green tea, oolong tea,black tea or the like, which is prepared from various syntheticaromachemicals, natural aromachemicals, natural essential oils, citrusoils, tea extract, animal aromachemicals, etc., there can be prepared aflavor composition or fragrance composition which is imparted with amild, deep, natural, fruity and tropical odor and further with a freshand widely accepted odor and which is enhanced in spreadability anddurability.

In the flavor composition or fragrance composition of the presentinvention, the amount of the active ingredient such as S-alkyl(R)-2-methylbutanethioate differs depending upon the kind and usepurpose of the flavor composition or fragrance composition; however, ingeneral, the preferred amount is, for example, 10⁻⁸ to 10⁹ ppb,preferably 10⁻⁷ to 10⁸ ppb, more preferably 10⁻⁶ to 10⁷ ppb in theflavor composition, and is, for example, 10⁻⁸ to 10⁹ ppb, preferably10⁻⁷ to 10⁸ ppb, more preferably 10⁻⁶ to 10⁷ ppb in the fragrancecomposition.

At least one kind of fixing agent used ordinarily may be added into theflavor composition or fragrance composition of the present invention.There may be used, for example, ethylene glycol, propylene glycol,dipropylene glycol, glycerine, hexylene glycol, benzyl benzoate,triethyl citrate, diethyl phthalate, Hercolyn, medium chain fatty acidtriglyceride, and medium chain fatty acid diglyceride.

By adding a flavor composition or fragrance composition containing theS-alkyl (R)-2-methylbutanethioate singly or in combination with theabove-mentioned other components, to, for example, a beverage, a food,an oral-care composition, a medicine, a fragrance product, a skin-carepreparation, a make-up cosmetic, a hair cosmetic, a sunblock cosmetic, amedicated cosmetic, a hair-care product, a soap, a body cleaner, a bathpreparation, a detergent, a fabric softener, a cleaning agent, a kitchencleaner, a bleaching agent, an aerosol, a deodorant-aromatic, or asundry, in an appropriate amount capable of imparting the unique flavorand/or fragrance of the S-alkyl (R)-2-methylbutanethioate, there can beprovided a product added with a flavor or a product added with afragrance.

As the product added with a flavor, there can be mentioned, beverages orfoods, for example, beverages such as fruit drink, fruit wine, lacticdrink, carbonated drink, refreshing drink, other drink and the like;ices such as ice cream, sherbet, ice candy and the like; Japanese-styleand Western-style confectioneries; jams; candies; jellies; gums; breads;luxury drinks such as coffee, cocoa, black tea, oolong tea, green teaand the like; soups such as Japanese-style soup, Western-style soup,Chinese-style soup and the like; condiments; instant drinks or foods;snacks; oral-care compositions such as dentifrice, oral cleaner, mouthwash, troche, chewing gum and the like; and medicines such as externalpreparation for skin (e.g. poultice or ointment), internal medicine andthe like.

As the product added with a fragrance, there can be mentioned, forexample, the followings.

There can be mentioned, as fragrance product, perfume, eau de parfum,eau de toilette, cologne, etc.; as skin-care preparation, face washingcream, vanishing cream, cleansing cream, cold cream, massage cream,milky lotion, toilet water, liquid foundation, pack, makeup remover,etc; as make-up cosmetic, foundation, face powder, pressed powder,talcum powder, lipstick, rouge, lip cream, cheek rouge, eye liner,mascara, eye shadow, eyebrow pencil, eye pack, nail enamel, enamelremover, etc.; and, as hair cosmetic, pomade, brilliantine, set lotion,hair stick, hair solid, hair oil, hair treatment, hair cream, hairtonic, hair liquid, hair spray, bandlin, hair growth agent, hairdye,etc.

There can be mentioned, as suntan cosmetic, suntan product, sunscreenproduct, etc.; as medicated cosmetic, antiperspirant, after shave lotionand gel, permanent wave agent, medicated soap, medicated shampoo,medicated skin cosmetic, etc.; as hair-care product, shampoo, rinse,rins-in-shampoo, conditioner, treatment, hair pack, etc.; as soap,toilet soap, bath soap, perfumed soap, transparent soap, synthetic soap,etc.; as body cleaner, body soap, body shampoo, hand soap, etc.; and, asbath preparation, bath preparations (e.g. bath salt, bath tablet andbath liquid), foam bath (e.g. bubble bath), bath oils (e.g. bath perfumeand bath capsule), milk bath, bath jelly, bath cube, etc.

There can be mentioned, as detergent, heavy-duty detergent for clothing,light-duty detergent for clothing, liquid detergent, washing soap,compact detergent, soap powder, etc.; as fabric softener, softener,furniture care, etc.; as cleaning agent, cleanser, house cleaner, toiletcleaner, bath cleaner, glass cleaner, mold remover, cleaner for wastepipe, etc.; as cleaner for kitchen, soap for kitchen, synthetic soap forkitchen, cleaner for dishes, etc.; as bleaching agent, oxidation typebleaching agent (e.g. chlorine-based bleaching agent or oxygen-basedbleaching agent), reduction type bleaching agent (e.g. sulfur-basedbleaching agent), optical bleaching agent, etc.; as aerosol, spray type,powder spray type, etc.; as deodorant-aromatic, solid type, gel type,liquid type, etc.; and, as sundry, tissue paper, toilet paper, etc.

When the flavor composition or fragrance composition of the presentinvention containing an S-alkyl (R)-2-methylbutanethioate as anessential component is used in a beverage, a food, an oral-carecomposition, a medicine, a fragrance product, a skin-care preparation, amake-up cosmetic, a hair cosmetic, a sunblock cosmetic, a medicatedcosmetic, a hair-care product, a soap, a body cleaner, a bathpreparation, a detergent, a fabric softener, a cleaning agent, a kitchencleaner, a bleaching agent, an aerosol, a deodorant-aromatic, a sundry,etc., the present flavor composition or fragrance composition can beused in any desired form meeting the intended application, selected fromthe followings. That is, the composition per se; a liquid form obtainedby dissolving the composition in, for example, an alcohol or apolyalcohol (e.g. propylene glycol or glycerine); a natural gum (e.g.gum arabic or tragacanth gum) form; an emulsion form obtained byemulsifying the composition with an emulsifier such as glycerine-fattyacid ester, saccharose-fatty acid ester, processed starch or the like; apowder form obtained by coating the composition with an excipient suchas natural gum (e.g. arabic gum), gelatin, dextrin or the like; asolution or dispersion form obtained by dissolving or dispersing thecomposition using a surfactant such as nonionic surfactant, anionicsurfactant, cationic surfactant, amphoteric surfactant or the like; amicro-capsule form obtained by treating the composition with a capsulingagent; and so forth.

The flavor composition or fragrance composition can also be used bybeing included in an inclusion agent (e.g. cyclodextrin) for stabilityand releasable state. The composition after inclusion is suited for theform of final product, such as liquid, solid, powder, gel, mist, aerosolor the like, and is appropriately selected and used.

The amount of S-methyl (R)-2-methylbutanethioate used in flavor-addedproduct (e.g. beverage, food, oral-care composition or medicine) isappropriately determined depending upon the effect and function expectedfor each product; however, the amount is generally about 10⁻⁹ to 10⁵ppb.

The amount of S-alkyl (R)-2-methylbutanethioate used in fragrance-addedproduct (e.g. fragrance product, skin-care preparation, make-upcosmetic, hair cosmetic, sunblock cosmetic, medicated cosmetic,hair-care product, soap, body cleaner, bath preparation, detergent,fabric softener, cleaning agent, kitchen cleaner, bleaching agent,aerosol, deodorant-aromatic or sundry) is appropriately determineddepending upon the effect and function expected for each product;however, the amount is generally about 10⁻⁹ to 10⁷ ppb.

Meanwhile, in the flavor-improving agent of the present invention,S-alkyl (S)-2-methylbutanethioates are used as an essential component.As specific examples of the S-alkyl (S)-2-methylbutanethioates, therecan be mentioned S-methyl ester, S-ethyl ester, S-n-propyl ester,S-isopropyl ester, S-butyl ester, S-2-methylpropyl ester, S-pentylester, S-2-methylbutyl ester, S-3-methylbutyl ester, S-hexyl ester,S-cis-3-hexenyl ester, S-heptyl ester and S-octyl ester of(S)-2-methylbutanethioic acid.

The S-alkyl (S)-2-methylbutanethioates may be used as an essentialcomponent in one kind or in two or more kinds. Of these compounds,preferred as the essential component of the flavor-improving agent ofthe present invention is S-methyl (S)-2-methylbutanethioate.

The S-alkyl (S)-2-methylbutanethioate used in the pre-sent invention maybe obtained by extraction from natural product, or by chemicalsynthesis. However, when the S-alkyl (S)-2-methylbutanethioate is usedin a large amount, it is preferably obtained by chemical synthesis.

For chemical synthesis of the S-alkyl (S)-2-methylbutanethioate, therecan be mentioned, as in the above-mentioned chemical synthesis ofS-alkyl (R)-2-methylbutanethioate, for example, a method of converting(S)-2-methylbutanoic acid (a raw material) into an acid halide and thenreacting it with an alkylthiol. For chemical synthesis of the(S)-2-methylbutanoic acid, there can be mentioned, for example, a methoddescribed in JP-A-1988-239245 or JP-A-1991-157346.

In the flavor-improving agent of the present invention, the S-alkyl(S)-2-methylbutanethioate obtained as above needs to have an opticalpurity of 70% e.e. or more.

The S-alkyl (S)-2-methylbutanethioate synthesized according to themethod described in JP-A-1988-239245 had a high optical purity of about75% e.e. A test was conducted to examine the optical purity of S-alkyl(S)-2-methylbutanethioate at which the (S) isomer begins to show itseffect. As a result, it was found that, in the present invention, the(S) isomer begins to show the effect at an optical purity of about 70%e.e. Accordingly, it was found that the (S)-thioesters having an opticalpurity of 70% e.e. or more can be used per se with no purification, asthe essential component of the present flavor-improving agent and canprovide a beverages or a food reliably giving a flavor and releasing anodor.

Here, the release of odor means not only a state in which the flavor ofbeverage or food spreads in the mouth in a moment, but also a state inwhich the odor of beverage or food is felt with the mere presence of thebeverage or food in the vicinity of the mouth.

In order to obtain an S-alkyl (S)-2-methylbutanethioate having anoptical purity of 70% e.e. or more, it is possible to appropriately mixan S-alkyl (S)-2-methylbutanethioate of high optical purity obtained bythe above-mentioned synthesis method, with a racemic S-alkyl2-methylbutanethioate which is known to be widely present in nature,particularly in fruits, beer, etc.

With respect to racemic S-alkyl 2-methylbutanethioates, it is knownthat, for example, S-methyl 2-methylbutanethioate is present in beer,hop, cheese, etc., S-ethyl 2-methylbutanethioate is present in durian,etc., and S-butyl 2-methylbutanethioate is present in galbanum, etc. Itis also known that S-n-propyl ester, S-isopropyl ester, S-butyl ester,S-2-methylpropyl ester, S-pentyl ester, S-2-methylbutyl ester,S-3-methylbutyl ester, S-hexyl ester, S-cis-3-hexenyl ester, S-heptylester, S-octyl ester, etc. of 2-methylbutanethioic acid are present invarious fruits, etc.

The flavor-improving agent of the present invention contains one or morekinds of the above-obtained S-alkyl (S)-2-methylbutanethioates having anoptical purity of 70% e.e. or more and, as necessary, other component(e.g. flavor), and is added to beverages or foods. The other component(e.g. flavor) used in the flavor-improving agent has no particularrestriction as long as it is used as an ordinary flavor for foods. Thecontent of the S-alkyl (S)-2-methylbutanethioate in the presentflavor-improving agent is not particularly restricted but is preferablyabout 1 to 15% by weight.

The beverage or food having an improved flavor, of the present inventioncontains the flavor-improving agent of the present invention whichcontains one or more kinds of S-alkyl (S)-2-methylbutanethioates havingan optical purity of 70% e.e. or more and, as necessary, other component(e.g. flavor), and is improved in flavor and release of odor. The amountof the present flavor-improving agent added to beverage or food can beappropriately varied depending upon the kind of the beverage or food;however, the amount (as S-alkyl (S)-2-methylbutanethioate) in beverageor food is about 10⁻⁸ to 10⁵ ppb (when reduced to optical purity 100%).When the addition amount is small (less than about 10⁻⁸ ppb), no cleareffect of addition is seen; and, when the addition amount is large (morethan about 10⁵ ppb), the flavor of beverage or food per se may beimpaired.

When the flavor-improving agent of the present invention is added to abeverage, in particular, the addition amount to the beverage ispreferably about 1 to 100 ppm in terms of S-alkyl(S)-2-methylbutanethioate.

The beverage or food to which the present flavor-improving agent isadded, may be any beverage or food as long as flavor improvement isexpected by the addition. There can be mentioned, as the food, cakes(e.g. caramel, candy, chocolate, chewing gum and baked sweet), ices(e.g. ice cream and sherbet), pudding, jelly, etc. As the beverage,there can be mentioned carbonated drinks (e.g. cider, lemon lime, fruitsoda, guarana and cola), fruit juice drinks free from any fruit juice orcontaining a natural fruit juice, nectar, concentrated syrup fordilution, lactic drinks, luxury drinks, functional drinks, alcoholicliquors having origins in Western countries (e.g. whisky and wine), etc.

EXAMPLES

The present invention is described in detail below by way of Examplesand Comparative Examples. However, the pre-sent invention is in no wayrestricted by them and can be changed as long as there is no deviationfrom the gist of the present invention.

Incidentally, in the Examples and Comparative Examples, odor wasexpressed referring to the expression made in “KORYO NO JISSAI CHISHIKI(Practical Knowledge of flavors or fragrances)” (1975, Mar. 25) writtenby Motoichi Indo, TOYO KEI-ZAI SHINPOSHA, page 3. Also in the Examplesand Comparative Examples, the units of formulations in Tables are partsby weight.

In the analyses in Examples, the following analytical apparatuses wereused.

Optical rotation:

-   -   DIP-370 (a product of JASCO corporation)        Proton NMR spectrum (¹H-NMR):    -   AM-400 (400 MHz) (a product of Brucker Bio-Spin GmbH)        Tetramethylsilane was used as an internal standard substance.        Infrared absorption spectrum (1R):    -   Nicolet Avatar 360 FT-IR (a product of Nicolet Japan)        Mass spectrum (MS):    -   M-80B mass spectrometer (ionization voltage: 20 V) (a product of        Hitachi, Ltd.)        Gas chromatography    -   HP-5890 (a product of Hewlett Packard)    -   The column used was PEG BC-WAX (0.25 mm×50 mm) (a product of GL.        Sciences Inc.).

Synthesis Example 1 Production of (R)-2-methylbutanoic acid

0.2 g (2 mmol) of tiglic acid and 20 ml of methanol were placed in a100-ml, stainless steel-made autoclave purged with nitrogen.Successively, there was placed 6.0 mg (0.007 mmol) ofRu[(+)-BINAP](BF₄)₂ {(+)-BINAP is(+)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl}. Hydrogenation wasconducted with stirring, at a hydrogen pressure of 4 kg/cm² at areaction temperature of 20° C. for 12 hours. The solvent was distilledoff to obtain 0.2 g (yield: 100%) of intended (R)-2-methylbutanoic acid.The optical rotation was [α]_(D) ²⁵=−16.7° (neat) and the purity by gaschromatography was 100%. The acid was reacted with(S)-1-phenylethylamine to synthesize an amide; and the amide wasanalyzed by gas chromatography. As a result, the optical purity of(R)-2-methylbutanoic acid was 88% e.e.

Synthesis Example 2 Production of (R)-2-methylbutanoic acid chloride

50.0 g (420 mmol) of thionyl chloride was dropwise added, at 50° C. in 3hours, to 35.8 g (350 mmol) of the (R)-2-methylbutanoic acid {[α]_(D)²⁵=−16.7° (neat)} obtained in Synthesis Example 1. Then, a reaction wasallowed to take place at 80° C. for 1 hour. Excessive thionyl chloridewas distilled off under reduced pressure. The residue was subjected todistillation under reduced pressure to obtain 40.4 g (yield: 96%) of(R)-2-methylbutanoic acid chloride.

Boiling point: 35° C./0.1 torr

¹H-NMR (CDCl₃):

-   -   0.98 (t, J=7.5 Hz, 3H), 1.29 (d, J=6.9 Hz, 3H), 1.58˜1.66 (m,        1H), 1.79˜1.87 (m, 1H), 2.78˜2.85 (m, 1H)

¹³C-NMR:

-   -   11.46 (CH₃), 16.88 (CH₃), 26.91 (CH₂), 53.29 (CH), 178.05 (CO)

Synthesis Example 3 Production of S-methyl (R)-2-methylbutanethioate

16.1 g (120 mmol) of the (R)-2-methylbutanoic acid chloride obtained inSynthesis Example 2 was dropwise added, in 1 hour with stirring, to a 0°C. mixture of 75 g of a 15% aqueous methylmercaptan solution and 100 mlof diethyl ether. The organic layer was separated and washed with anaqueous sodium chloride solution. The diethyl ether was distilled off.The residue was concentrated under reduced pressure to obtain 15.1 g(yield: 86%) of S-methyl (R)-2-methylbutanethioate. The product wasanalyzed by gas chromatography. As a result, the chemical purity was100% and the optical purity was 88% e.e.

Boiling point: 32° C./5 torr

[α]_(D) ²⁰: −36.7° (neat)

¹H-NMR (CDCl₃):

-   -   0.92 (t, J=7.5 Hz, 3H), 1.29 (d, J=6.9 Hz, 3H), 1.43˜1.52 (m,        1H), 1.70˜1.78 (m, 1H), 2.28 (s, 3H), 2.54˜2.60 (m, 1H)

¹³C-NMR:

-   -   11.29 (CH₃), 11.58 (CH₃), 17.21 (CH₃), 27.17 (CH₂), 50.04 (CH),        204.22 (CO)

Example 1 Evaluation of Fragrance or Flavor

Each of the S-methyl (R)-2-methylbutanethioates obtained in SynthesisExamples was put on a bottle mouth and filter paper, and sensoryevaluation was carried out by perfumers or flavorists having 5 years ormore of experience. The evaluation results are shown in Table 1.

TABLE 1 Compound name Odor characteristics S-methyl (R)-2- A beautiful,fresh, highly- methylbutanethioate taste, unique, strong odor whichreminds a strong, fresh passion fruit. S-methyl 2- An odor which isnatural but methylbutanethioate (racemic is low in strength and hasform)* slight other smells. *a product of Oxford Chemicals

As seen above, the S-methyl (R)-2-methylbutanethioate used in the flavorcomposition or fragrance composition of the present invention had abeautiful, fresh, highly-taste, unique, strong flavor and fragrancewhich reminded a strong, fresh passion fruit. Meanwhile, all theperfumers or flavorists pointed out that the racemic S-methyl2-methylbutanethioate had an odor which was natural but was low instrength and had slight other smells.

Example 2

The S-methyl (R)-2-methylbutanethioate synthesized based on the methoddescribed in JP-A-1988-239245 had a high optical purity of about 88%e.e. A test was conducted to examine the optical purity of S-methyl(R)-2-methylbutanethioate at which the (R) isomer begins to show itseffect reliably. Racemic S-methyl 2-methylbutanethioate was mixed withS-methyl (R)-2-methylbutanethioate in various proportions to prepare (R)dominant compositions of different optical purities. Using these (R)dominant compositions, the optical purity of S-methyl(R)-2-methylbutanethioate at which the effect of the (R) isomer could beclearly felt, was measured by applying a 2:2 point identification testdescribed in 54 page of “Kanno Kensa Nyumon (Introduction to SensoryTest)” (Sato Makoto) published by K.K. Nikka Giren Shuppansha on Oct.16, 1978. In the method, two kinds of samples A and B are distinguishedfrom each other as follows. That is, the samples A and B are presentedto panelers as distinct samples and their characteristics are memorizedby the panelers; then, the samples A and B are presented to them asblind samples to allow them to pick up a sample different from thesample A; this operation is repeated a plurality of times; thereby, thedifference between the samples is judged based on the number of correctanswers obtained.

As a result, it was found that S-methyl (R)-2-methylbutanethioate, whenhaving an optical purity of 50% e.e. or more, can be used per se withoutbeing purified, for preparation of a flavor or fragrance compositionreliably improved in flavor or fragrance.

Example 3 and Comparative Example 1

The S-methyl (R)-2-methylbutanethioate obtained in the SynthesisExamples was added to a grapefruit flavor composition shown in Table 2,to prepare a flavor composition of Example 3 containing the effectiveingredient at a concentration of 0.01 ppb. Racemic S-methyl2-methylbutanethioate was added to the same grapefruit flavorcomposition to prepare a flavor composition of Comparative Example 1.The two flavor compositions were subjected to an organoleptic test byflavorists each having an experience of at least 5 years.

TABLE 2 Comparative Component Example 3 Example 1 Grape fruit essence95.0 95.0 Ethyl butanoate 0.1 0.1 Ethyl 2-methylbutanoate 0.02 0.02Octanal 0.01 0.01 Nootkatone 0.05 0.05 S-methyl (R)-2- 0.000001 —methylbutanethioate Racemic S-methyl 2- — 0.000001 methylbutanethioateEthanol Balance Balance Total 100.0 100.0

As a result, it was pointed out by all the flavorists that the flavorcomposition of Example 3 was imparted with a natural, deep, fresh flavornot possessed by the flavor composition of Comparative Example 1.

Example 4 Production of Fragrance Composition for Shampoo Formulation 1

Component Benzyl salicylate 55 L-citronellol 10 Ethyl acetoacetate 5Galaxolide 50BB* (a product of IFF) 390 Geraniol 10 Hedione (a productof Firmenich S.A.) 120 Heliobouquet 8 (a product of TakasagoInternational Corporation) 10% cis-3-hexen-1-ol solution in DPG** 10 10%cis-3-hexenyl acetate solution in DPG 5 Hexylcinnamic aldehyde 50β-ionone 17 Kovanol 40 (a product of Takasago International Corporation)Lemon oil 40 Linalool 45 Linalyl acetate 45 Nerolidol 55 Phenylethylalcohol 30 Phenylethyl cinnamate 5 Santalex T 35 (a product of TakasagoInternational Corporation) 10% Triplal solution in DPG (a product ofIFF) 5 1% maltol solution in DPG 15 10 ppm S-methyl(R)-2-methylbutanethioate 5 solution in DPG Total 1000 *Benzyl benzoate**Dipropylene glycol

Comparative Example 2

A fragrance composition for shampoo was prepared in the same formulationas in Example 4 except that, in the formulation of Example 4, the 10 ppmS-methyl (R)-2-methylbutanethioate solution in DPG was replaced by a 10ppm racemic S-methyl (R)-2-methylbutanethioate solution in DPG.

Application Example 1 Production of Shampoos

The following components including the fragrance composition forshampoo, prepared in Example 4 or Comparative Example 2 were stirred at80° C. with stirring, until a uniform material were obtained. Then, theuniform material was cooled to 35° C. to prepare a shampoo. Thefragrance of each shampoo was evaluated by a sensory test by fiveperfumers each having an experience of least 5 years.

[Shampoo composition (mass %)] Sodium laurate 40.00 DisodiumN-cocoyl-N-carboxymethylethyl-N- 10.00 carboxymethylethylenediamimeCoconut oil fatty acid diethanolamide (2) 2.00 Butylene glycol 2.00Citric acid 0.35 Sodium chloride 0.10 Methylparaben 0.20 Propylparaben0.10 Tetrasodium edetate 0.10 Fragrance composition of Example 4 orComparative Example 2 0.50 Purified water Balance Total 100.00

Evaluation Results of Example 4 and Comparative Example 2

The fragrances of the shampoos of Example 4 and Comparative Example 2were evaluated. As a result, all the perfumers pointed out that thefragrance of the shampoo using the Example 4 formulation containingS-methyl (R)-2-methylbutanethioate was superior in spreadability andgave a fresh and natural feeling.

Example 5 Production of Fragrance Composition for Body ShampooFormulation 2

Component Lemon oil 100 Lime oil 180 Geranyl nitrile 10 10% aldehyde C-8solution in DPG 25 10% aldehyde C-10 solution in DPG 35 Ethyl decanoate12 Triplal (a product of IFF) 3 10% isocyclocitral solution in DPG (aproduct of IFF) 25 Styrallyl acetate 20 α-terpineol 30 Linalool 70Linalyl acetate 50 Geraniol 60 Geranyl acetate 5 Lilial (a product ofGivaudan S.A.) 80 Hexyl cinnamic aldehyde 120 Myrac aldehyde (a productof IFF) 15 Cis-3-hexenyl salicylate 15 β-ionone 25 Heliotropin 5Tonalide(a product of PFW) 30 Dipropylene glycol Balance 10 ppm S-methyl(R)-2-methylbutanethioate solution in DPG 5 Total 1000

Comparative Example 3

A fragrance composition for body shampoo was prepared in the sameformulation as in Example 5 except that, in the formulation of Example5, the 10 ppm S-methyl (R)-2-methylbutanethioate solution in DPG wasreplaced by a 10 ppm racemic S-methyl 2-methylbutanethioate solution inDPG.

Application Example 2 Production of Body Shampoos

Body shampoos were prepared using the fragrance compositions for bodyshampoo, prepared in Example 5 and Comparative Example 3. The fragranceof each body shampoo was evaluated by a sensory test by five perfumerseach having an experience of least 5 years.

[Body shampoo formulation (mass %)] Dibutylhydroxytoluene 0.05Methylparaben 0.10 Propylparaben 0.10 Tetrasodium edetate 0.10 Potassiumchloride 0.20 Glycerine 5.00 Coconut oil fatty acid diethanolamide (2)3.00 Sodium polyoxyethylene lauryl ether acetate (3E.O.) (30%) 10.00Coconut oil fatty acid amide propyl betaine solution (34%) 25.00Potassium myristate (40%) 25.00 Fragrance composition of Example 5 orComparative Example 3 0.50 Purified water Balance Total 100.00

Evaluation results of Example 5 and Comparative Example 3

The fragrances of the body shampoos of Example 5 and Comparative Example3 were evaluated. As a result, all the perfumers pointed out that thefragrance of the body shampoo using the Example 5 formulation containingS-methyl (R)-2-methylbutanethioate gave an improved freshness and acitrus feeling.

Example 6 Production of Rosy Fragrance Composition Formulation 3

Component α-pinene 8 Aldehyde C-16 1 Allyl amyl glycolate 1Ambrettolide(a product of IFF) 8 Bergamot 15 Carbitol 100 Cardamon oil 3L-citronellol 30 β-Damascone 2 10% dimethyloctanol solution in DPG 4Dipropylene glycol 29 10% Dynascone solution in DPG 5 10% ethyl acetatesolution in DPG 4 Ethyl acetoacetate 15 10% galbanum oil solution in DPG10 Hedione(a product of Firmenich S.A.) 195 Heliobouquet 10 (a productof Takasago International Corporation) Cis-3-hexen-1-ol 2 10%cis-3-hexen-1-ol solution in DPG 3 β-ionone 10 Jasmine absolute 3 10%lime oil solution in DPG 5 Linalyl acetate 40 10% 8-mercaptomenthonesolution in DPG 8 Musk T 200 (a product of Takasago InternationalCorporation) Nerolidol 46 Phenylethyl alcohol 17 β-pinene 117 Rhubofix(aproduct of Firmenich S.A.) 12 Rose absolute 3 10% rose oil solution inDPG 5 10% L-rose oxide solution in DPG 15 Santalex T 40 (a product ofTakasago International Corporation) Triplal (a product of IFF) 14Veloutone(a product of Firmenich S.A.) 12 Maltol 5 10 ppm S-methyl(R)-2-methylbutanethioate solution in DPG 5 Total 1000

Comparative Example 4

A rosy fragrance composition was prepared in the same formulation as inExample 6 except that, in the formulation of Example 6, the 10 ppmS-methyl (R)-2-methylbutanethioate solution in DPG was replaced by a 10ppm racemic S-methyl 2-methylbutanethioate solution in DPG.

Application Example 3 Production of Cosmetic Creams

Cosmetic creams were prepared using the rosy fragrance compositionsprepared in Example 6 and Comparative Example 4. The fragrance of eachcosmetic cream was evaluated by a sensory test by five perfumers eachhaving an experience of least 5 years.

[Cosmetic cream (mass %)] Stearyl alcohol 6.0 Stearic acid 2.0Hydrogenated lanolin 4.0 Squalane 9.0 Octyl decanol 10.0 Glycerine 6.0Polyethylene glycol 1500 4.0 Polyoxyethylene (25) cetyl ether 3.0Glycerine monostearate 2.0 Methylparaben Appropriate amount EthylparabenAppropriate amount Fragrance composition of 0.1 Example 6 or ComparativeExample 4 Purified water Balance Total 100.0

Evaluation results of Example 6 and Comparative Example 4

The fragrances of the cosmetic creams of Example 6 and ComparativeExample 4 were evaluated. As a result, all the perfumers pointed outthat the odor the cosmetic cream using the Example 6 formulationcontaining S-methyl (R)-2-methylbutanethioate had high spreadability andgave a natural feeling.

Flavors of beverages containing S-methyl (S)-2-methylbutanethioate(namely, the flavor-improving agents of the present invention), andracemic forms thereof (namely, conventional flavors) were compared witheach other.

(1) Selection of Panelers

In the same manner as in Example 1 were selected total 10 expertflavorists (8 males and 2 females) of twenties to thirties.

(2) Preparation of Flavor-Improving Agent for Beverage, by Recombinationof Formulation

A racemic S-alkyl 2-methylbutanethioate in a conventional flavorformulation was replaced by a corresponding (S) isomer to prepare aflavor-improving agent for beverage.

(3) Addition to Beverage

The flavor-improving agent prepared in the above (2) was added to amodel beverage; and the flavors when the (S) isomer and the racematewere added, were compared with each other.

Synthetic Example 4 Production of (S)-2-methylbutanoic acid

0.2 g (2 mmol) of tiglic acid and 20 ml of methanol were placed in a100-ml, stainless steel-made autoclave purged with nitrogen.Successively, there was placed 6.0 mg (0.007 mmol) ofRu[(−)-BINAP](BF₄)₂ {(−)-BINAP is(−)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl}. Hydrogenation wasconducted with stirring, at a hydrogen pressure of 4 kg/cm² at areaction temperature of 20° C. for 12 hours. The solvent was distilledoff to obtain 0.2 g (yield: 100%) of intended (S)-2-methylbutanoic acid.The optical rotation was [α]_(D) ²⁵=+16.7° (neat) and the purity by gaschromatography was 100%. The acid was reacted with(R)-1-phenylethylamine to synthesize an amide; and the amide wasanalyzed by gas chromatography. As a result, the optical purity of(S)-(+)-2-methylbutanoic acid was 88% e.e.

Synthesis Example 5 Production of (S)-2-methylbutanoic acid chloride

50.0 g (420 mmol) of thionyl chloride was dropwise added, at 50° C. in 3hours, to 35.8 g (350 mmol) of the (S)-2-methylbutanoic acid {[α]_(D)²⁵=+16.7° (neat)} obtained in Synthetic Example 1. Then, a reaction wasallowed to take place at 80° C. for 1 hour. Excessive thionyl chloridewas distilled off under reduced pressure. The residue was subjected todistillation under reduced pressure to obtain 40.4 g (yield: 96%) of(S)-2-methylbutanoic acid chloride.

Boiling point: 35° C./0.1 torr

¹H-NMR (CDCl₃):

-   -   0.98 (t, J=7.5 Hz, 3H), 1.29 (d, J=6.9 Hz, 3H), 1.58˜1.66 (m,        1H), 1.79˜1.87 (m, 1H), 2.78˜2.85 (m, 1H)

¹³C-NMR:

-   -   11.46 (CH₃), 16.88 (CH₃), 26.91 (CH₂), 53.29 (CH), 178.05 (CO)

Synthesis Example 6 Production of S-methyl (S)-2-methylbutanethioate

16.1 g (120 mmol) of the (S)-2-methylbutanoic acid chloride obtained inSynthesis Example 2 was dropwise added, in 1 hour with stirring, to a 0°C. mixture of 75 g of a 15% aqueous methylmercaptan solution and 100 mlof diethyl ether. The organic layer was separated and washed with anaqueous sodium chloride solution. The diethyl ether was distilled off.The residue was concentrated under reduced pressure to obtain 15.1 g(yield: 86%) of S-methyl (S)-2-methylbutanethioate. The product wasanalyzed by gas chromatography. As a result, the chemical purity was100% and the optical purity was 88% e.e.

Boiling point: 32° C./5 torr

[α]_(D) ²⁰: +36.7° (neat)

¹H-NMR (CDCl₃):

-   -   0.92 (t, J=7.5 Hz, 3H), 1.29 (d, J=6.9 Hz, 3H), 1.43˜1.52 (m,        1H), 1.70˜1.78 (m, 1H), 2.28 (s, 3H), 2.54˜2.60 (m, 1H)

¹³C-NMR:

-   -   11.29 (CH₃), 11.58 (CH₃), 17.21 (CH₃), 27.17 (CH₂), 50.04 (CH),        204.22 (CO)

Example 7 and Comparative Example 5 Evaluation of Flavor

Each of the S-methyl (S)-2-methylbutanethioate obtained in SynthesisExamples was put on a bottle mouth and filter paper, and sensoryevaluation was carried out by the above-mentioned panelists. Theevaluation results are shown in Table 3.

TABLE 3 Compound name Odor Characteristics S-methyl (S)-2- A odor whichreminds the methylbutanethioate fruity-note having slight fresh-leafy.And a very clear, spreading odor which is similar to the full ripenessof fruit. S-methyl 2- An odor which is natural but methylbutanethioate(racemic is low in strength and has form)* slight other smells. *aproduct of Oxford Chemicals

As seen above, the S-methyl (S)-2-methylbutanethioate used in theflavor-improving agent of the present invention had a odor which remindsthe fruity-note having slight fresh-leafy. And a very clear, spreadingodor which is similar to the full ripeness of fruit. Meanwhile, theracemic form had a odor which was natural but was low in strength andhad slight other smells.

Example 8 and Comparative Example 6

Flavor-improving agents for beverage were prepared based on thestrawberry flavor formulations shown in Table 4. The flavor-improvingagent of Example 8 used the formulation containing the S-methyl(S)-2-methylbutanethioate obtained in Synthesis Example 6, and theflavor-improving agent of Comparative Example 6 used the formulationcontaining racemic S-methyl 2-methylbutanethioate. Theseflavor-improving agents for beverage were each added to a fruitjuice-free carbonated drink containing 10% by weight of glucose and 0.1%by weight of citric acid, in an amount of 0.1% by weight. Each of theresultant drinks was evaluated for odor by the above-mentioned panelers.The results are shown in Table 5.

TABLE 4 Comparative Component Example 8 Example 6 S-methyl(S)-2-methylbutanethioate 2.000 — S-methyl 2-methylbutanethioate(racemic — 2.000 form) Ethyl butyrate 1.200 1.200 Isoamyl butyrate 0.1400.140 Butyric acid 0.900 0.900 Ethyl lactate 0.040 0.040 Benzyl alcohol2.000 2.000 Cis-3-hexenol 1.000 1.000 Linalool 0.100 0.100 Ethylmethylphenylglicidate 0.120 0.120 Hexanal 0.080 0.0803-Ethoxy-2-methyl-4-pyrone 1.500 1.500 γ-decalactone 0.170 0.170γ-undecalactone 0.140 0.140 Ethyl alcohol (95%) 55.610 55.610 Propyleneglycol Balance Balance 100.000 100.000

TABLE 5 Evaluation of Sample Odor release of odor A drink to which the Avery clear, 10 persons flavor-improving agent spreading odor of Example1 containing which is similar S-methyl (S)-2-methyl to the full ripenessbutanethioate was added of fruit. (Example 8) A drink to which the Noclear odor  0 person flavor-improving agent which is similar ofComparative Example to the full ripeness 1 containing S-methyl of fruitand 2-methylbutanethioate which is felt when (racemic form) was the (S)isomer has added (Comparative Example been added. 6) *Evaluation ofrelease of odor indicates the number of persons who gave evaluation of“superior to other sample”.

As seen in Table 5, the drink to which the flavor-improving agent forbeverage, of Example 8 containing S-methyl (S)-2-methylbutanethioate wasadded, had a very clear, spreading odor which was similar to the fullripeness of fruit. Meanwhile, the drink to which the flavor-improvingagent for beverage, of Comparative Example 6 containing S-methyl2-methylbutanethioate (racemic form) was added, gave no freshness feltin addition of S-methyl (S)-2-methylbutanethioate.

Example 9

The S-methyl (S)-2-methylbutanethioate synthesized based on the methoddescribed in JP-A-1988-239245 had a high optical purity of about 88%e.e. A test was conducted to examine the optical purity of S-methyl(S)-2-methylbutanethioate at which the (S) isomer begins to show itseffect reliably. Racemic S-methyl 2-methylbutanethioate was mixed withS-methyl (S)-2-methylbutanethioate in various proportions to prepare (S)dominant compositions of different optical purities. Using these (S)dominant compositions, the optical purity of S-methyl(S)-2-methylbutanethioate at which the effect of the (S) isomer could beclearly felt, was measured by applying a 2:2 point identification methoddescribed in 54 page of “Kanno Kensa Nyumon (Introduction to sensoryTest)” (Sato Makoto) published by K.K. Nikka Giren Shuppansha on Oct.16, 1978. In the method, two kinds of samples A and B are distinguishedfrom each other as follows. That is, the samples A and B are presentedto panelers as distinct samples and their characteristics are memorizedby the panelers; then, the samples A and B are presented to them asblind samples to allow them to pick up a sample different from thesample A; this operation is repeated a plurality of times; thereby, thedifference between the samples is judged based on the number of correctanswers obtained.

As a result, it was found that S-methyl (S)-2-methylbutanethioate, whenhaving an optical purity of 70% e.e. or more, can be used per se withoutbeing purified, for the reliable improvement of the flavor of beverageor food.

1. A flavor composition or fragrance composition and a flavor-improvingagent, characterized by comprising an optically active S-alkyl2-methylbutanethioate as an active ingredient.
 2. A flavor compositionor fragrance composition characterized by comprising an S-alkyl(R)-2-methylbutanethioate as an active ingredient.
 3. A flavorcomposition or fragrance composition according to claim 2, wherein theS-alkyl (R)-2-methylbutanethioate has an optical purity of 50% e.e. ormore.
 4. A flavor composition or fragrance composition according toclaim 1, which is a flavor composition.
 5. A flavor compositioncharacterized by comprising an S-alkyl (R)-2-methylbutanethioate at aconcentration of 10⁻⁵ to 10⁷ ppb.
 6. A product added with a flavor by aflavor composition set forth in claim
 5. 7. A flavor-added productaccording to claim 6, which is one member selected from beverages,foods, oral-care compositions and medicines.
 8. A product added with aflavor, characterized by being obtained by adding an S-alkyl(R)-2-methylbutanethioate at a concentration of 10⁻⁹ to 10⁵ ppb.
 9. Aflavor composition or fragrance composition according to claim 1, whichis a fragrance composition.
 10. A fragrance composition characterized bycomprising an S-alkyl (R)-2-methylbutanethioate at a concentration of10⁻⁶ to 10⁷ ppb.
 11. A product added with a fragrance by a fragrancecomposition set forth in claim
 10. 12. A fragrance-added productaccording to claim 11, which is one member selected from fragranceproducts, skin-care preparations, make-up cosmetics, hair cosmetics,sunblock cosmetics, medicated cosmetics, hair-care products, soaps, bodycleaners, bath preparations, detergents, fabric softeners, cleaningagents, kitchen cleaners, bleaching agents, aerosols,deodorant-aromatics, repellants and sundries.
 13. A product added with afragrance, characterized by being obtained by adding an S-alkyl(R)-2-methylbutanethioate at a concentration of 10⁻⁹ to 10⁷ ppb.
 14. Amethod for intensification, improvement or modification of flavor orfragrance, characterized by adding an S-alkyl (R)-2-methylbutanethioate.15. A flavor-improving agent characterized by comprising, as an activeingredient, an S-alkyl (S)-2-methylbutanethioate having an opticalpurity of 70% e.e. or more.
 16. A flavor-improving agent according toclaim 15, wherein the S-alkyl (S)-2-methylbutanethioate is S-methyl(S)-2-methylbutanethioate.
 17. A beverage or food having an improvedflavor, characterized by comprising an S-alkyl (S)-2-methylbutanethioatehaving an optical purity of 70% e.e. or more, at a proportion of 10⁻⁸ to10⁵ ppb when reduced to 100% optical purity.
 18. A beverage or foodhaving an improved flavor according to claim 17, wherein the S-alkyl(S)-2-methylbutanethioate is S-methyl (S)-2-methylbutanethioate.